A decanter centrifuge of the type described above is known from JP 11-179236 that describes energy recovery by providing at the discharge opening of the bowl of the centrifuge a weir plate with an arcuate wall extending in a direction perpendicular to the weir plate. The arcuate wall is displaced from the edge of the discharge opening. Furthermore, the arcuate wall extends in a direction opposite the direction of rotation of the bowl. Generally, in decanter centrifuges, the liquid phase is discharged away from the decanter centrifuge into a sump.
WO 94/27726 discloses a centrifugal separator having a vertically aligned axis of rotation, in which energy is recovered by providing in the outlet chamber of the centrifugal separator a plate with a central hole and having closed channels extending axially from the plate towards the top of the outlet chamber and radially from the central hole towards the rim of the plate with a radius of curvature being, essentially in each point, smaller than the curve of an involute of a substance discharged through said central hole. The axis of rotation of the centrifugal separator extends through the centre of the central hole of the plate. Generally this arrangement is provided at the transition of the liquid from one liquid chamber to another within the centrifugal separator.
A problem with the known decanter centrifuge is that energy contained in the discharged substance, generally being a liquid, is lost in the transition between hole and wall. Particularly, discharged substance flowing over the overflow edge of the weir plate tends to cling to the outside of the weir plate thereby being accelerated which is energy consuming thus causing energy loss.
Further, the feed is accelerated to a rotational speed on entering into the bowl and the energy thus consumed is lost when the liquid phase exits over a weir at the outlets in the base plate. The decanter centrifuge of above-mentioned JP 11-179236 seeks to regain the lost energy by providing the said arcuate wall. However, the amount of energy thereby regained remains relatively small. There is, in other words, still a significant amount of energy lost in the separation process.
In one aspect, the present invention therefore aims at providing a decanter centrifuge that eliminates or reduces the problems mentioned above, thereby obtaining an improved energy recovery.